Fusarium oxysporum is an ascomycetous fungus that is well-known as a soilborne plant pathogen. In addition, a large population of nonpathogenic
F. oxysporum (NPF) inhabits various environmental niches, including the phytosphere. To obtain an insight into the origin of plant pathogenic
F. oxysporum, we focused on the tomato (
Solanum lycopersicum) and its pathogenic
F. oxysporum f. sp.
lycopersici (
FOL). We collected
F. oxysporum from wild and transition
Solanum spp. and modern cultivars of tomato in Chile, Ecuador, Peru, Mexico, Afghanistan, Italy, and Japan, evaluated the fungal isolates for pathogenicity, VCG, mating type, and distribution of
SIX genes related to the pathogenicity of
FOL, and constructed phylogenies based on ribosomal DNA intergenic spacer sequences. All
F. oxysporum isolates sampled were genetically more diverse than
FOL. They were not pathogenic to the tomato and did not carry
SIX genes. Certain NPF isolates including those from wild
Solanum spp. in Peru were grouped in
FOL clades, whereas most of the NPF isolates were not. Our results suggested that the population of NPF isolates in
FOL clades gave rise to
FOL by gaining pathogenicity.
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